1. Field of the Invention
The present invention relates to the field of thin film formation and more particularly to a method and apparatus for forming silicon nitride films at low deposition temperatures and high deposition rates.
2. Discussion of Related Art
Modern integrated circuits are made up of literally millions and millions of transistors integrated together into functional circuits. In order to further increase the computational power or storage capability of integrated circuits, transistor feature size such as gate length and gate oxide thickness must be further scaled down. Unfortunately, as transistor gate lengths are continually scaled, the transistors electrical characteristics and performance can greatly change due to thermal redistribution of dopants in the device. As such, as devices are further scaled, the thermal budget used to manufacture the integrated circuit must also be reduced to insure consistent and reliable electrical performance of the device. That is, as device dimensions continue to shrink, the deposition and process temperatures used to form the thin films of the integrated circuit must also be reduced. The manufacture of integrated circuits having transistor dimensions of 65 nanometer technology and below are expected to require high quality thin films which can be formed at deposition temperatures of less than 550° C.
Additionally, in order to further scale the semiconductor device, the thin films used to make the devices must be able to be formed with high compositional and thickness uniformity. In order to form films with extremely uniform thickness and composition the films generally need to be formed in single wafer deposition reactors. In order to form thin films in a single wafer reactor in a manufacturable amount of time their deposition rate should be at least 50 Å per minute.
Silicon nitride thin films deposited by thermal chemical vapor deposition (CVD) are used throughout the semiconductor fabrication processes. For example, thermal CVD silicon nitride films are used as spacer films, etch stops, as well as capacitor and interpoly dielectrics. Unfortunately, present techniques of forming high quality silicon nitride films in a single wafer reactor utilizing thermal chemical vapor deposition require high deposition temperatures of greater than 750° C. and/or have low deposition rates at lower temperatures. In most silicon nitride deposition processes, if the deposition temperature is decreased to less than 550° C. the deposition rate is greatly reduced and can go to zero. Additionally, when silicon nitride films are deposited at low temperatures or at high deposition rate the quality of the film is generally poor.
Thus, what is needed is a method of forming a high quality silicon nitride film by thermal chemical vapor deposition (CVD) at low deposition temperature, less than or equal to 550° C. and at a manufacturable deposition rate of greater than 50 Å per minute.